The Fantech SHR 1504 Heat Recovery Ventilator (HRV), boasting of a 3-speed ventilation control, offers airflow up to 149 CFM and effectively serves 3-5 bedroom homes. It has external dry contacts for facilitating speedy connection of remote controls. The HRV keeps your home ventilated at optimal levels by simultaneously supplying and exhausting the same amount of pure and impure air. During winter, it supplies warm air by utilizing the heat of the exhausted air stream, thus saving huge amounts of energy. It also supplies pre-cooled air in the summer, if your home is fitted with an air cooling system. A preset defrost cycle is triggered when the incoming air stream reaches temperatures of 23 F and below. During the defrost cycle, the supply air is stopped and the speed at which exhausting air is expelled is increased to achieve better defrosting. After few minutes, the HRV returns to normal operation and then the cycle continues.